1. Field of the Invention
The present invention relates to a projection type liquid crystal display device which synthesizes a plurality of color rays of light modulated based on video data into one image and projects the synthetic light thus produced onto a screen to display the image, and an optical block for use in such a projection type liquid crystal display device.
This application claims the priority of the Japanese Patent Application No. 2003-322300 filed on Sep. 12, 2003, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
FIG. 1 shows a projection type liquid crystal display device by way of example. This projection type liquid crystal display device, indicated with a reference 100, is a sol-called “three-panel” type liquid crystal projector. That is, the projection type liquid crystal display device 100 uses three liquid crystal display panels corresponding to three primary colors (red, green and blue), respectively.
As shown in FIG. 1, the liquid crystal projector 100 includes three polarizing beam splitters 101R, 101G and 101B, liquid crystal display panels 102R, 102G and 102B, synthesizing prism 103, projection lens 104 and a screen S′. In the liquid crystal display projection 100, light emitted from a light source such as a lamp or the like is split into three color rays of light corresponding to three primary colors, respectively. The split red light (R), green light (G) and blue light (B) are guided by the polarizing beam splitters 101R, 101G and 101B, respectively, to the liquid crystal panels 102R, 102G and 102B, respectively, which will modulate the incident red light (R), green light (G) and blue light (B), respectively, on the basis of video data. The modulated red light (R), green light (G) and blue light (B) are synthesized by the synthesizing prism 103 into one image. The synthetic light thus produced is projected through the projection lens 104 onto the screen S′ on which it will be displayed as a color image in a larger scale.
Note here that each of the liquid crystal display elements used as the liquid crystal display panels 102R, 102G and 102B, respectively, is generally of either a transmission or reflection type. The transmission type liquid crystal display element will modulate light from a back light disposed at the back thereof for transmission. On the other hand, the reflection type liquid crystal display element will modulate incident light for reflection. There being demands for a projector with a higher definition of display, more compact design and a higher brightness, the reflection type liquid crystal display element has been attracting more and more attention and applied in practice as a promising display device that can be designed to display with a higher definition and have a more compact structure and also can utilize light with a higher efficiency.
More specifically, the reflection type liquid crystal display element includes a glass substrate having provided thereon a transparent electrode formed from an electrically conductive material such as ITO (Indium-Tin Oxide), a drive circuit board having provided thereon reflection pixel electrodes formed from an aluminum-based metallic material and a liquid crystal layer filled between the glass substrate and drive circuit board which are disposed opposite to each other and sealed all along the edges thereof with a sealing member. Also, each of the surfaces of the glass substrate and drive circuit board, opposite to each other, has provided thereon an alignment film to align the liquid crystal in a predetermined direction.
In the reflection type liquid crystal display element, a voltage is applied between the transparent electrode and reflection pixel electrodes opposite to each other to apply an electric field to the liquid crystal layer. Then, the liquid crystal layer is varied in optical characteristic correspondingly to a potential difference between the electrodes to modulate the light passing by the liquid crystal layer. Therefore, the reflection type liquid crystal display element can assign intensity levels by the light modulation.
The liquid crystals used as such a liquid crystal display element include a twisted nematic liquid crystal (will be referred to as “TN liquid crystal” hereunder) whose dielectric anisotropy (a difference Δε(=ε(∥)−ε(⊥)) between a dielectric constant ε(∥) parallel to the long axis of liquid crystal molecules and dielectric constant ε(⊥) perpendicular to the long axis of the liquid crystal molecules) goes positive. This TN liquid crystal is also called “horizontally-aligned liquid crystal”. In the TN liquid crystal, when applied with no drive voltage, liquid crystal molecules are aligned being nearly horizontally twisted in relation to the substrate, and provide a display in white in a so-called “normally white display mode”. On the other hand, when applied with a drive voltage, the liquid crystal molecules are erected perpendicularly to the substrate and provides a display in black. Also in the TN liquid crystal, since it is necessary to preset a direction in which the liquid crystal molecules are to be erected when applied with a drive voltage, so a constant direction is pretilted through about several to 10 deg. in practice.
Also in these days, an liquid crystal display element using a vertically-aligned liquid crystal in which nematic liquid crystal having a negative dielectric anisotropy is vertically aligned has been attracting attention because of its high contrast and speed of response. In this vertically-aligned liquid crystal, when applied with no drive voltage, the liquid crystal molecules are aligned nearly perpendicularly to the substrate and provide a display in black in a so-called “normally black display mode”. On the other hand, when applied with a drive voltage, the liquid crystal molecules are tilted in a predetermined direction to have the light transmittance thereof varied due to a birefringence developed at that time of tilting.
Also, in the vertically-aligned liquid crystal, since the contrast will not be uniform as shown in FIGS. 2 and 3 unless liquid crystal molecules 200 are tilted in the same directions, so it is necessary to vertically align the liquid crystal by tilting the long axis of the liquid crystal molecules 200 through a slight pretilt angle θ in a constant direction X in relation to a line normal to a drive circuit board 202 having pixel electrodes 201 formed thereon. The pretilted direction X, that is, the direction in which the liquid crystal molecules 200 are aligned, is set nearly diagonal to a device whose transmittance is normally caused to be maximum by a combination with an optical system such as a polarization plate and the like, namely, in a direction of about 45 deg. that is a nearly diagonal direction of the pixel electrodes 201 laid in the form of a nearly square matrix. Also, if the pretilt angle θ is too large, the vertical alignment will be deteriorated, the black level will rise to lower the contrast and the V−T (drive voltage−transmittance) curve will be adversely affected. Therefore, the pretilt angle θ is normally controlled to fall within a range of 1 to 5 deg.
The alignment film which pretilts the vertically-aligned liquid crystal is an obliquely evaporated membrane formed by depositing an inorganic material such as silicon dioxide (SiO2) or the like obliquely onto a substrate or a polymer membrane of polyimide or the like having a rubbed surface. The pretilting and pretilt angle are controlled by controlling the direction of incidence and evaporation angle for the obliquely-evaporated membrane or by controlling the rubbing direction and conditions for the polymer membrane. Normally, the practical pretilt angle is about 45 to 65 deg. in relation to the light normal to the substrate.
In the above Liquid crystal projector 100, if red, green and blue images for representation by the three liquid crystal display panels 102R, 102G and 102B are synthesized as they are because of the limited geometry of the liquid crystal display panels 102R, 102G and 102B in relation to the synthesizing prism 103 when the color rays of light (R, G and B) modulated by the liquid crystal display panels 102R, 102G and 102B, respectively, are synthesized by the synthesizing prism 103 into one image as shown in FIG. 1, only the green image modulated by the liquid crystal display panel 102G will be displayed being horizontally inverted in relation to the red and blue images modulated by the other liquid crystal display panels 102R and 102B, respectively (as indicated with references A and A′, respectively, in FIG. 1).
That is, the green light (G) modulated by the liquid crystal display panel 102G is incident upon the projection lens 104 after passing by the dichroic surface of the synthesizing prism 103, while the red light (R) and blue light (B) modulated by the liquid crystal display panels 102R and 102B, respectively, will be incident upon the projection lens 104 after being reflected by the dichroic surface of the synthesizing prism 103 (as indicated with a solid line and dashed line, respectively, in FIG. 1).
On this account, normally, depending upon which the number of times the color rays of light (R, G and B) modulated by the three liquid crystal display panels 102R, 102G and 102B, respectively, are reflected until they are synthesized is, odd or even (including zero), an image modulated by one (102G) of the three liquid crystal display panels 102R, 102G and 102B is displayed being horizontally inverted in relation to the images modulated by the other two liquid crystal display panels (102R and 102B) (cf. the Japanese Published Unexamined Patent Application No. 2867992).
Therefore, in the aforementioned Liquid crystal projector 100, the green image modulated by the liquid crystal display panel 102G shown in FIG. 4B is displayed being horizontally inverted in relation to the red and blue images modulated by the liquid crystal display panels 102R and 102B, respectively, shown in FIG. 4A, so that the images synthesized by the synthesizing prism 103 will coincide with each other on the screen S′.
Note here that in the aforementioned conventional liquid crystal projector 100, when a leftward-ascending oblique line L in black is displayed in a white display on the screen S′ as shown in FIG. 5, the oblique line L which should appear black will be displayed in a color which will be resulted from mixing of black and magenta as the case may be. Also, when a rightward-ascending oblique line in black is displayed in the white display on the screen S′ in addition to the leftward-ascending line L, the oblique line L which should appear black will be displayed in greenish black in some cases. In any of these cases, the oblique line will possibly be stained with any other color, which will considerably lower the quality of an image display.